Rolling Mill and Method for Controlling a Rolling Mill

ABSTRACT

A rolling mill, in particular, a cold strip tandem rolling mill, for producing a metal strip, with a number of stands is arranged in a tandem path, wherein, in a direction of production of the metal strip, a first stand is designed as driving stand and serves as inlet for a section of the tandem path, in which a primary thickness reduction of the metal strip occurs, and by corresponding control of the driving stand, an increase in the mechanical inlet tension of the metal strip can be achieved. In a method for controlling a rolling mill, in particular, a cold strip tandem rolling mill, for producing a metal strip, in a production direction of the metal strip, a first stand is controlled as driving stand, the driving stand achieving a significant increase in the mechanical inlet tension on the metal strip and a significant thickness reduction of the metal strip.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a United States national phase filing under 35 U.S.C. §371 of International Application No. PCT/EP2007/059066, filed Aug. 30, 2007 which claims priority to German Patent Application No. 10 2006 048 427.4, filed Oct. 12, 2006. The complete disclosure of the above-identified application is hereby fully incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a rolling mill, in particular a cold-strip tandem rolling mill, and to a method for controlling such a rolling mill. The invention relates, furthermore, to the use of a first stand of a rolling mill, in particular of a cold-strip tandem rolling mill.

BACKGROUND

One objective of the distribution of pass reductions in rolling mills, particularly in cold-strip tandem rolling mills, may also be, as well as the distribution of the pass reductions for technological reasons, a distribution of the pass reductions according to the mechanical engineering circumstances of the individual roll stands, in order to utilize these optimally in terms of production.

In discontinuous tandem mill trains which use as entry material both longitudinally divided hot strips and strips from hood-type annealing processes in which the coils are wound with low strip tension for technological reasons, it may therefore happen that the first stand of the tandem mill train can apply only low rolling power.

In order to distribute the overall pass reduction in the rolling mill according to the technological requirements or so as to optimize the overall pass reduction even with regard to the first roll stand, it is necessary that this first stand can furnish the desired rolling power. An increase in the rolling power of the roll stand can be achieved in two ways, to be precise by increasing the rolling force and/or by increasing the tensile stresses in the metal strip.

An increase in the rolling force can therefore take place by means of an increase in the system pressure of the hydraulic screwdown and/or an enlargement of a piston area of a screwdown cylinder. In existing mills, limits are often placed on these possibilities, or an appropriate increase in the volume force is not possible. Reasons for this are, for example, that the operating pressure is already close to the permissible pressure limit, and an increase is therefore no longer possible, or that an enlargement of the piston area, that is to say the installation of a new screwdown cylinder, cannot be carried out for reasons of installation space. Furthermore, an increase in the rolling force may fail because the existing stand columns can no longer absorb the additional forces.

The increase in an entry-side strip tension upstream of the first stand of the tandem mill train in the production direction may also take place by the installation of an S-roll (bridle), of a tension or multiple-roll bridle or of a two-high roll stand. In existing mills, these possibilities likewise often have placed on them limits which are predetermined by structural circumstances (space requirements) or by technological parameters, such as oiled metal strips.

SUMMARY

According to various embodiments, an improved rolling mill, in particular an improved cold-strip tandem rolling mill, and also an improved method for controlling such a rolling mill can be specified. In particular, the rolling mill should have a low space requirement and have an improved controllability of a strip run. Furthermore, according to various embodiments, an existing rolling mill, in particular an existing cold-strip tandem rolling mill, can be retrofit so that this can be operated by means of the control method according to an embodiment.

According to an embodiment, a rolling mill, in particular a cold-strip tandem rolling mill for the production of a metal strip, may have a plurality of stands arranged in a tandem mill train, a first stand in a production direction of the metal strip being designed as a driving stand and serving as the entry for a section of the tandem mill train in which a main thickness reduction of the metal strip takes place, and an increase in a mechanical entry tension of the metal strip being achievable by means of a corresponding activation of the driving stand.

According to a further embodiment, a thickness reduction of the metal strip may be implementable by means of the driving stand, but this thickness reduction being dispensed with essentially in favor of an increase in the mechanical entry tension of the metal strip. According to a further embodiment, the driving stand or its supporting and/or working rolls may be, during the rolling of the metal strip, at least partially:—drivable in the production direction of the metal strip, this drive preferably being lower than that of a stand following in the production direction;

—operable as a generator; and/or—drivable opposite to the production direction. According to a further embodiment, the driving stand may be operable in such a way that essentially no slip occurs between a working roll of the driving stand and the metal strip. According to a further embodiment, a second stand in the production direction of the metal strip may be designed as a first actively rolling roll stand, by means of which a first substantial thickness reduction of the metal strip can be implemented. According to a further embodiment, the rolling mill may have downstream of the first actively rolling roll stand in the production direction of the metal strip at least one following actively rolling roll stand. According to a further embodiment, the rolling mill may have no assembly preceding the tandem mill train and may have an action increasing the strip tension, hence, for example, no S-roller arrangement, no tension bridle and/or no two-high stand. According to a further embodiment, the rolling mill may have directly upstream of the entry stand, opposite to the production direction of the metal strip, with the exception of a deflecting roller, an uncoiler. According to a further embodiment, a last stand of the rolling mill may be designed as a driving stand. According to a further embodiment, the first stand and the last stand may be operable alternately as a driving stand and as an actively rolling roll stand for a reversing operation of the rolling mill.

According to another embodiment, a retrofitted rolling mill, in particular a retrofitted cold-strip tandem rolling mill, may be implemented having upstream of a tandem mill train in the production direction of a metal strip no assembly with the function of increasing the strip tension, and the retrofitted rolling mill being designed as described above.

According to a further embodiment, an assembly with the function of increasing the strip tension may be demounted.

According to yet another embodiment, a roll installation or rolling mill train, in particular a cold rolling installation or cold rolling mill train, may have a rolling mill, preferably a cold-strip tandem rolling mill, as described above.

According to yet another embodiment, in a method for activating a rolling mill, in particular a cold-strip tandem rolling mill, for the production of a metal strip, a first stand in a production direction of the metal strip may be activated as a driving stand, a significant increase in the mechanical entry tension for the metal strip taking place by means of the driving stand, on the one hand, and, on the other hand, no appreciable thickness reduction of the metal strip being carried out.

According to a further embodiment, the driving stand or its supporting and/or working rolls being, during the rolling of the metal strip, may be at least partially:—driven in the production direction of the metal strip, this drive preferably being lower than that of a stand following in the production direction;—operated as a generator; and/or—driven opposite to the production direction. According to a further embodiment, the driving stand in the production direction of the metal strip may be operated in such a way that essentially no slip occurs between a working roll of the driving stand and the metal strip. According to a further embodiment, a second stand in the production direction of the metal strip may be designed as a first actively rolling roll stand, by means of which a first substantial thickness reduction of the metal strip is carried out. According to a further embodiment, a last stand of the rolling mill may be designed as a driving stand. According to a further embodiment, the first stand and the last stand may be operated alternately as a driving stand and as an actively rolling roll stand for a reversing operation of the rolling mill.

According to yet another embodiment, in a use of a first stand, in a production direction of a metal strip, of a rolling mill, in particular of a cold-strip tandem rolling mill, as a driving stand for the rolling mill, a significant increase in the mechanical entry tension for the metal strip may take place by means of the driving stand.

According to a further embodiment, the driving stand can be designed as described above. According to a further embodiment, the rolling mill can be operated or may be operable by means of a method as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below by means of exemplary embodiments, with reference to the accompany drawing in which:

FIG. 1 shows a cold-strip tandem rolling mill according to the prior art for continuous operation, and

FIG. 2 shows a cold-strip tandem rolling mill according to an embodiment likewise for continuous operation.

DETAILED DESCRIPTION

In rolling mills which have to cover a broad product spectrum in terms of material strength and of overall degree of delamination, further factors arise whereby a distribution of the rolling power to the individual roll stands can take place. In the individual roll stands of the rolling mill, a high rolling power is normally available, since the respective roll stands are designed for a maximum forming.

According to various embodiments, preferably in the case of low required overall degrees of delamination, an available or installed rolling power is utilized to the effect that the individual reductions in the roll stands are distributed to the stands such that the first stand of the mill train (entry stand) in a production direction of a metal strip assumes the function of a driving stand for increasing the entry tension. According to various embodiments, the driving stand then serves mainly for increasing the entry tension of the metal strip, and the overall degree of delamination for the metal strip is distributed to the remaining stands of the rolling mill by a distribution of a respective pass reduction.

If, for example, an overall degree of delamination to be implemented in a five-stand rolling mill lies at 10% of a metal strip thickness, then, in the case of a linear apportionment of the overall degree of delamination to the remaining four roll stands of the mill train, in a general distribution each roll stand would take over only approximately 2.5% delamination. That is to say, instead of a respective delamination of 2% in the case of fivefold successive rolling, according to various embodiments the overall degree of delamination is distributed to the four roll stands which follow the driving stand and which in each case have to take over only 0.5% more delamination. According to various embodiments, therefore, a redistribution of the rolling power to the roll stands following the entry/driving stand in the production direction occurs.

According to various embodiments, a saving of additional assemblies having the function of increasing the strip tension is obtained by utilizing an existing roll stand for increasing the entering strip tension, and improved strip guidance is also obtained. The better strip guidance affords an improved controllability and stabilization of a strip run of the metal strip by an equalization of the tensile forces as a result of a decoupling of eccentricities of a coil at an uncoiler.

The rolling mill according to various embodiments has a plurality of roll stands in a tandem train, a roll stand set up for delamination being designed as an assembly with the function of increasing the strip tension, as what is known as a driving stand.

Furthermore, according to various embodiments, a control method for a rolling mill is made available, a roll stand being activated in such a way that it functions for the metal strip as an assembly with the function of increasing the strip tension.

According to various embodiments, the rolling mill is configured to the effect or operated to the effect that a delamination of the metal strip may take place by means of the driving stand, but this delamination is essentially dispensed with, and an increase in the mechanical entry tension of the metal strip takes place by means of the driving stand.

The increase in the mechanical entry tension of the metal strip is obtained by means of a suitable operation of the driving stand. This is, for example, a generator operation in which the rolls of the driving stand are not driven. Furthermore, it is possible to drive the rolls of the driving stand to the effect that the working and/or the supporting rolls of the driving stand are driven opposite to the production direction of the metal strip. Moreover, it is possible to drive the working and/or supporting rolls in such a way that they move the metal strip forward in the production direction, although this drive is lower than a drive of an actively rolling roll stand following in the production direction. In this case, no slip or, if this cannot be implemented, as little slip as possible should occur between the metal strip and the working rolls and also between the supporting and the working rolls of the driving stand.

In one embodiment, a first actively rolling roll stand of the rolling mill is a roll stand which is second in the production direction of the metal strip. A first substantial thickness reduction of the metal strip takes place by means of this first actively rolling roll stand. That is to say, also, the driving stand is a first stand of the rolling mill in the production direction of the metal strip, preferably a first stand of a tandem rolling mill.

According to various embodiments, the rolling mill is characterized in that it has no S-roll arrangement, no tension or multiple-roll bridle and also no two-high roll stand preceding the tandem mill train.

It is therefore possible, according to various embodiments, to convert an already existing rolling mill correspondingly. According to various embodiments, this takes place in that an existing S-roll arrangement or a tension or multiple-roll bridle or a two-high roll stand of the rolling mill is demounted, and the first stand of the tandem mill train is operated as a driving stand with the function of increasing the strip tension.

Furthermore, some embodiments relate to a (retrofitted) rolling installation, in particular a (retrofitted) cold rolling installation with a (retrofitted) rolling mill, preferably with a (retrofitted) cold-strip tandem rolling mill. This rolling installation has on the entry side, as an assembly with the function of increasing the strip tension, preferably only a single roll stand of the tandem mill train, which roll stand is operated correspondingly as a driving stand with the function of increasing the strip tension. That is to say, the rolling installation according to various embodiments has no S-roll arrangement, no tension or multiple-roll bridle and also no two-high roll stand.

The following statements refer to a cold-strip tandem rolling mill with a metal-strip entry section 10 configured according to various embodiments and with a tandem mill train 20 set up according to various embodiments. In this case, in particular, the tandem mill train 20 is operated or activated differently, as compared with the prior art, thus having effects on the metal-strip entry section 10 of the cold-strip tandem rolling mill 1. That is to say, in the metal-strip entry section 10, an assembly 260 with the function of increasing the strip tension becomes obsolete (FIG. 1). However, the invention is not to be restricted to cold-strip tandem rolling mills 1, but is to relate in general to tandem mill trains 20. In this context, a tandem mill train 20 is understood to mean a roll stand arrangement which is constructed from at least two roll stands 220; 230; 240; 250 which are connected in series, preferably connected directly in series, in a production direction P of a metal strip 100. That is to say, also, the invention can be employed in a two-stand mill train.

FIG. 1 shows two or three essential sections of a conventional cold-strip tandem rolling mill 1, specifically the metal-strip entry section 10 and the tandem mill train 20 following the latter in the production direction P of the metal strip 100. Furthermore, located in the cold-strip tandem rolling mill 1 is a metal-strip exit section (not illustrated in the drawing) which, for example, has a coiler for a reversing operation or further assemblies, such as, for example, a skin-pass/leveling mill train, following the cold-strip tandem rolling mill 1.

The metal-strip entry section 10 of the cold-strip tandem rolling mill 1 has a coil 110 which is seated exchangeably on an uncoiler 270 and can be unwound and the metal strip 100 of which enters the tandem mill train 20 (corresponding here to an actively rolling region 25 of the rolling mill 1) of the cold-strip tandem rolling mill 1 via an assembly 260 with the function of increasing the strip tension and via a deflecting roller 210. To build up or to increase a mechanical entry tension of the metal strip 100 by means of the assembly 260 with the function of increasing the strip tension, said assembly is designed as an S-roller or an S-roller arrangement (bridle) or a tension or multiple-roller bridle or as what is known as a driver (two-high roll stand).

Bridle units guide and straighten the metal strip 100 and maintain its internal tensile stresses, in that, for example, adjustable rollers arranged above the strip run of the metal strip 100 can be lowered by means of a mechanical drive out of an initial position onto a strip surface into a working position. The strip bent alternately in the working position of a multiple-roller bridle unit leaves the bridle unit at a working roll located nearest to a roll nip of the assigned roll stand 220, and level with a run-through line of the roll stand (not illustrated in the drawing). In the illustrated exemplary embodiment of the prior art, in FIG. 1, the assembly 260 with the function of increasing the strip tension is designed as an S-roller arrangement (bridle).

The tandem mill train 20 has a plurality of roll stands 220; 230; 240; 250 which all function as actively rolling roll stands 220; 230; 240; 250. That is to say, during the rolling of a metal strip 200, an appreciable thickness reduction of a metal strip 100 takes place at all the roll stands 220; 230; 240; 250 of the rolling mill 1. That is to say, a first stand 220 (also called an entry stand) of the tandem mill train 20 is also at the same time a first actively rolling roll stand 230.

In an embodiment illustrated in FIG. 2, then, the tandem mill train 20, which may conform in its set-up to that shown in the prior art, is activated in another way. This gives rise to a metal-strip entry section 10 modified according to various embodiments and therefore to a differently constructed rolling mill 1 according to various embodiments, in particular a differently constructed cold-strip tandem rolling mill 1 according to various embodiments.

Overall, in the tandem rolling mill 1 according to various embodiments, instead of an additional assembly 260 with the function of increasing the strip tension, the first stand 220 of the tandem mill train 20 is used in the function of a driver, in order to implement a build-up of mechanical tension in the metal strip 100, in front of the actual actively rolling region 25 (section 25 of the tandem mill train 20 in which a main thickness reduction of the metal strip 100 takes place) of the tandem mill train 20 in the production direction P of the metal strip 100. Since, according to various embodiments, the build-up of mechanical tension can take place in the first stand 220 of the tandem mill train 20 in the production direction P of the metal strip 100, an assembly 260 with the function of increasing the strip tension, such as is illustrated, for example, by the S-roller arrangement in FIG. 1, becomes obsolete. According to various embodiments, the first stand 220 only has its function changed, and therefore the second stand 230 in the production direction P within the tandem mill train 20 constitutes the first actively rolling stand 230.

The cold-strip tandem rolling mill 1 according to various embodiments has a metal-strip entry section 10 according to various embodiments with an uncoiler 270 and with a deflecting roller 210. The tandem mill train 20 according to various embodiments has a plurality of roll stands 220, 260; 230; 240; 250, only the roll stands 230; 240; 250 arranged downstream of the first stand 220 being actively rolling roll stands. The first stand 220 in the production direction P of the metal strip 100 is designed as an assembly 260 with the function of increasing the strip tension. This first stand 220 is designated below as a driving stand 260 which in this case is no longer actively rolling, but serves mainly for increasing the mechanical strip tension of the metal strip 100. It is possible, however, to operate this driving stand 260 as an actively rolling roll stand 220, 260, which may be advantageous particularly for a reversing operation of a reversing rolling mill (see also below) or else if a high thickness reduction is required for a metal strip 100.

In order to implement in the driving stand 260 a function in which strip tension is increased, the rolls of the driving stand 260, which is preferably designed as a four-high roll stand, exerts a force on the metal strip 100 which, in a static situation acts essentially perpendicularly on a surface (side of sheet-like form) of the metal strip 100. When the rolling mill 1 is in operation, this force exerted on the metal strip 100 is not sufficient to leave behind a substantial plastic deformation in the metal strip 100. A large part of the deformation of the metal strip 100 caused by the driving stand 260 is in this case of an elastic nature.

In order, then, to give the driving stand 260 the function of increasing the strip tension, three operating modes of the driving stand 260 are possible. This is illustrated by the dotted or dashed arrows in the driving stand 260 in FIG. 2.

Thus, for example, it is possible to operate the driving stand 260 as a generator. In this case, all or only one or a plurality of rolls of the driving stand 260 may run as a generator. Other rolls may, for example, be driven with a right-hand or left-hand run. Preferably, however, in this case all the rolls of the driving stand 260 run as a generator. As a result, a force directed opposite to the production direction P in the metal band 100 acts on the latter, so as to build up in the metal strip 100, downstream of the driving stand 260 in the production direction P, tensile stresses which enable a following second stand (first actively rolling stand) 230 and further following stands 240; 250 to achieve an effective degree of delamination.

Furthermore, it is possible to drive the driving stand 260 motively in the right-hand or left-hand run. In this case, the right-hand or the left-hand run is to relate to the working rolls of the driving stand 260. The supporting rolls of the driving stand 260 are operated in the correspondingly opposite direction of rotation or run as a generator. Thus, on the one hand, it is possible to drive the working rolls of the driving stand 260 in such a way that these rotate opposite to the production direction P in the region of a “roll nip” (tangential component). When the rolling mill 1 is in operation, these working rolls, of course, rotate in the opposite direction, since the force on the working roll arising from the metal strip 100 is higher than the drive force of the working rolls themselves. That is to say, the working rolls and, if appropriate, the assigned supporting rolls rotate in the same way as the corresponding rolls of an active roll stand 230; 240; 250 following in the production direction P.

Moreover, it is possible to drive the working rolls of the driving stand 260 in the same direction of rotation as the corresponding working rolls of a following actively rolling roll stand 230; 240; 250. In this case, however, it is preferable if these are operated with a lower force than the following actively rolling roll stands 230; 240; 250, in order to give the metal strip 100 inherent tensile stresses. The supporting rolls of the driving stand 260 may be operated correspondingly. In this case, it is again possible to drive only a fraction of the rolls correspondingly. The other rolls may be operated, for example, as a generator.

Care must be taken to ensure that the rolls of the driving stand 260 with respect to one another and also the working rolls of the driving stand 260 with the metal strip 100 have as little slip as possible, preferably no slip at all. That is to say, in particular, an activation of the driving stand 260 to increase the mechanical entry tension of the metal strip 100 takes place in such a way that an outer circumferential speed of the respective working roll of the driving stand 260 corresponds essentially to a translational speed of the metal strip 100, and these two speed vectors come into congruence in the “roll nip” of the driving stand 260. This also applies similarly to the supporting rolls of the driving stand 260. In one embodiment, the slip between the metal strip 100 and a working roll of the driving stand 260 amounts to approximately 0.1% to 0.75%, preferably 1% to 2%, particularly 3% to 5% and, particularly preferably, 6% to 10%. That is to say, the outer circumferential speed of the working roll of the driving stand 260 is preferably slower by the amount of these percentages than the speed of the metal strip 100. In further embodiments, however, no slip occurs.

Furthermore, a driven or generator operating mode, of whatever type, of the rolls in the driving stand 260 may be envisaged. It is possible, for example, to drive only the supporting rolls of the driving stand 260 and operate its working rolls as a generator. It is also possible to drive only those rolls of the driving stand 260 which are located on one side of the metal strip 100 and to run those on the other side as a generator.

The invention can be used in all rolling mills 1. This applies both to rolling mills 1 newly to be designed and to already existing rolling mills 1 which are converted according to various embodiments. The same applies similarly to the method for operating the rolling mill 1. In the case of rolling mills 1 to be retrofitted, the assembly 260 with the function of increasing the strip tension is demounted, and a roll stand of the tandem mill train 20 is operated according to various embodiments as a driving stand 260. The retrofitted rolling mill 1 thereby acquires shorter dimensions, with the result that, for example, other assemblies can be installed in the rolling mill 1 or rolling installation 1.

Furthermore, the invention can be used both for continuously operated rolling mills 1 (FIG. 2) and also for rolling mills 1 operated in a reversing mode (merely indicated in FIG. 2).

A reversing roll in mill 1, in turn, has, at its rear end lying opposite the metal-strip entry section 10, a deflecting roller 210 and a coiler on which a coil 110 can be wound.

In a rolling mill 1 operated in reversing mode (bracketed illustration in FIG. 2), it is preferable if, after a first run-through of the metal strip 100 through the tandem mill train 20, a last stand 250 of the tandem mill train 20 is activated or operated in the same way as a driving stand 260 according to various embodiments for a second run-through of the metal strip 100. The first stand 220 functioning as a driving stand 260 in the first run-through is then preferably activated as the last actively rolling roll stand 250 in the second run-through of the metal strip 100. In a third run-through, this is once again reversed. That is to say, in the reversing rolling mill 1, both the first stand 220 and the last stand 250 (reference symbols for the first run-through of the metal strip 100) can in each case be operated or used as a driving stand 260 and, for a following run-through of the metal strip 100, also as the last actively rolling stand 250.

In a reversing mill, however, it is also possible to operate the first stand (220/250) and the last stand (250/220) in each case alternately as driving stands 260 (first stand) and at the same time not to activate or to cause to co-rotate the other last stand in each case, without assigning a relevant function to the latter.

The invention can be used particularly in already existing cold-strip tandem rolling mills 1 which cover a broad bandwidth of a production spectrum with regard to an overall degree of delamination, or can be used particularly in those rolling mills 1 which have rolling power reserves (also for a maximum required delamination) in the individual roll stands. This then gives rise to a use of the first actively rolling roll stand 220; (250) as a driving stand 260 which does not carry out any essential delamination of the metal strip 100. The possible pass reduction lost as a result is distributed to the remaining roll stands (220); 230; 240; 250 of the rolling mill 1. By the first stand 220; (250) being used as a driving stand 260, a stabilization and equalization of the strip run due to decoupling from the uncoiler 270; improved strip guidance, particularly in the case of a wedge-shaped narrow strip; and an increase in the entering strip tension take place. (Reference symbols in brackets refer to reversing operation of a reversing rolling mill 1 according to various embodiments)

According to various embodiments, by the strip tension for the metal strip 100 being increased, a possible pass reduction lost by the driving stand 260 can be compensated within the tandem mill train 20, so that the tandem mill train 20 according to various embodiments or the rolling mill 1 according to various embodiments can implement the same thickness reductions as a tandem mill train 20 according to the prior art. A shorter length of the overall mill is particularly advantageous in this case, since the assembly 260 with the function of increasing the strip tension (see FIG. 1) can be dispensed with. This also affords a lower outlay in terms of maintenance in addition to a lower energy consumption.

According to various embodiments, the first stand 220 in the production direction P of the metal strip 100 does not necessarily have to be designed or activated as a driving stand 260 after the metal strip 100 has entered the tandem mill train 20. It is likewise possible to apply the invention to another roll stand or a plurality of roll stands 220; 230; 240; 250 of the rolling mill 1. Thus, for example, it is possible, particularly in the case of a comparatively long tandem mill train 20, also to design or activate as a driving stand 260, in addition to the first stand 220, a roll stand 230; 240; 250 which is arranged further to the rear in the production direction P.

Furthermore, it is possible to apply the invention to the last roll stand 250 in the production direction P, in order to increase the strip tension of the metal strip 100 upstream of this. For this purpose, the last roll stand 250, 260 in the production direction P is driven, the outer circumferential speed of the working rolls of the last roll stand 250, 260 (driving stand 260) being slightly higher than the speed of the metal strip 100; or the last stand 250, 260 is driven with a higher drive power than a roll stand 220; 230; 240 arranged upstream in the production direction P. That is to say, also, the slip values given above are to be applied in reverse; hence, the outer circumferential speed of the working rolls of the last roll stand 250, 260 is preferably higher by the amount of the percentage given above than the speed of the metal strip 100 in the “roll nip” of the last roll stand 250, 260.

In FIG. 2 of the drawing, the roll stands 220; 230; 240; 250; 260 of the tandem mill train 20 are depicted as four-high stands. However, the invention is not to be restricted to four-high stands, but is to relate to all forms of construction of actively rolling roll stands 220; 230; 240; 250; 260. The invention can therefore also be applied, for example, to actively rolling two-high or six-high roll stands. 

1. A rolling mill, in particular a cold-strip tandem rolling mill for the production of a metal strip, comprising a plurality of stands arranged in a tandem mill train, wherein a first stand in a production direction of the metal strip is designed as a driving stand and serves as the entry for a section of the tandem mill train in which a main thickness reduction of the metal strip takes place, and wherein an increase in a mechanical entry tension of the metal strip being achievable by means of a corresponding activation of the driving stand.
 2. The rolling mill according to claim 1, wherein a thickness reduction of the metal strip is implementable by means of the driving stand, but this thickness reduction being dispensed with essentially in favor of an increase in the mechanical entry tension of the metal strip.
 3. The rolling mill according to claim 1, wherein, the driving stand or at least one of its supporting and working rolls are, during the rolling of the metal strip, at least partially one of: drivable in the production direction of the metal strip, this drive being lower than that of a stand following in the production direction; operable as a generator; and drivable opposite to the production direction.
 4. The rolling mill according to claim 3, wherein the driving stand is operable in such a way that essentially no slip occurs between a working roll of the driving stand and the metal strip.
 5. The rolling mill according to claim 1, wherein a second stand in the production direction of the metal strip is designed as a first actively rolling roll stand, by means of which a first substantial thickness reduction of the metal strip can be implemented.
 6. The rolling mill according to claim 5, wherein the rolling mill having downstream of the first actively rolling roll stand in the production direction of the metal strip at least one following actively rolling roll stand.
 7. The rolling mill according to claim 1, wherein the rolling mill has no assembly preceding the tandem mill train and has an action increasing the strip tension, or at least one of no S-roller arrangement, no tension bridle and no two-high stand.
 8. The rolling mill according to claim 1, wherein the rolling mill has directly upstream of the entry stand, opposite to the production direction of the metal strip, with the exception of a deflecting roller, an uncoiler.
 9. The rolling mill according to claim 1, wherein a last stand of the rolling mill is designed as a driving stand.
 10. The rolling mill according to claim 10, wherein the first stand and the last stand are operable alternately as a driving stand and as an actively rolling roll stand for a reversing operation of the rolling mill.
 11. A retrofitted rolling mill or a retrofitted cold-strip tandem rolling mill, the retrofitted rolling mill implemented having upstream of a tandem mill train in the production direction of a metal strip no assembly with the function of increasing the strip tension, and the retrofitted rolling mill being designed as claimed in claim
 1. 12. The retrofitted rolling mill according to claim 11, wherein an assembly with the function of increasing the strip tension is demounted.
 13. A roll installation or rolling mill train, in particular a cold rolling installation or cold rolling mill train, comprising a rolling mill, preferably a cold-strip tandem rolling mill, as claimed in claim
 1. 14. A method for activating a rolling mill, in particular a cold-strip tandem rolling mill, for the production of a metal strip, the method comprising the step of: activating a first stand in a production direction of the metal strip as a driving stand, wherein a significant increase in the mechanical entry tension for the metal strip takes place by means of the driving stand, on the one hand, and, on the other hand, no appreciable thickness reduction of the metal strip is carried out.
 15. The method according to claim 14, wherein the driving stand or at least one of its supporting and working rolls are, during the rolling of the metal strip, at least partially one of: driven in the production direction of the metal strip, this drive preferably being lower than that of a stand following in the production direction; operated as a generator; and driven opposite to the production direction.
 16. The method according to claim 14, wherein the driving stand in the production direction of the metal strip is operated in such a way that essentially no slip occurs between a working roll of the driving stand and the metal strip.
 17. The method according to claim 14, wherein a second stand in the production direction of the metal strip is designed as a first actively rolling roll stand, by means of which a first substantial thickness reduction of the metal strip is carried out.
 18. The method according to claim 14, wherein a last stand of the rolling mill is designed as a driving stand.
 19. The method as claimed in claim 18, the first stand and the last stand is operated alternately as a driving stand and as an actively rolling roll stand for a reversing operation of the rolling mill.
 20. A method comprising the step of using a first stand, in a production direction of a metal strip, of a rolling mill, or a cold-strip tandem rolling mill, as a driving stand for the rolling mill, wherein a significant increase in the mechanical entry tension for the metal strip takes place by means of the driving stand.
 21. The method according to claim 20, wherein the driving stand is designed as a first stand in a production direction of the metal strip and serves as the entry for a section of the tandem mill train in which a main thickness reduction of the metal strip takes place, and wherein an increase in a mechanical entry tension of the metal strip being achievable by means of a corresponding activation of the driving stand.
 22. The method according to claim 20, wherein the rolling mill being operated or being operable by means of a method comprising the step of: activating a first stand in a production direction of the metal strip as a driving stand, wherein a significant increase in the mechanical entry tension for the metal strip takes place by means of the driving stand, on the one hand, and, on the other hand, no appreciable thickness reduction of the metal strip is carried out. 